Power line carrier system



July 21', 1936. rH. A. AFFEL Er AL. 2,048,092

\ POWER LINE ,CARRIER SYSTEM .Original Filed Deo. l2, 1930 Main ine INVENTRS `ATTORNEY Patented July 21, 1936 muri-:D STATES PATENT ori-ica 'i 2,048,092 y i POWER LINE CARRIER SYSTEM Herman A. Ael, Ridgewood, and Estiil I. Green,

East Orange, N. J., assignors to American Telephone and Telegraph Company, a corporation of New York Original application December 12. 1930, Serial No. 501,984. `Divided and this application Becamber 9, 1932, Serial No. 646,532

7 Claims. (Cl. 177-352) isolatea section of power line vfrom its branches at carrier frequencies.

'I'his is a division of the applicants' copending application, Serial No. 501,984, filed December 12,

1930, and is intended to cover more specically theA forms of networks shown in Figures 1 to 3, of the` resultingfrom the complex nature of the power line connections and also from the improper terminating impedances cause a carrier circuit, superimposed upon such a power line, to have characteristics that are extremely erratic in the range of frequencies employed. Furthermore,

switching operations in the power system will have an important effect upon the carrier frequency characteristics.

For example, let it be assumed lthat a carrier.

system is superimposed upon a power transmission line that has a spur connection at a point along the main transmission line between the ter-` minals-of the carrier system. Unless such spur line is isolated from the main line in some way or is terminated in an impedance approximating its' characteristic impedance, the carrier fre- -quency impedance that ispresented by the spur line-will vary widely with frequency and at certain frequencies will resemble a short circuit, thus that may 'be connected in series with each wire of preventing satisfactory transmission between the carrier terminals. The employment of anti-resonant circuits or choke coils has been suggested as a remedy to prevent the disturbing effect produced by suchdetrimental paths. Such choke circuits have the disadvantage that their impedance varies with frequency and that they may require tuning to the working frequency.

'Ihis invention resides, in part, in a network ,when a highfrequency termination is desired at currents in that apparatus. Networks l0' and which the :improvementsset: forth Other objects of this invention will be apparent from the following description when read in connection with the attached drawing, o'f which Figure 1 shows schematically a transmission line adapted for the simultaneous transmission of 5- power currents and carrier signaling currents embodying the series impedance network referred to hereinbefore; Figs. 2 and 3 show schematically other impedance networks that may be substituted for the impedance 'network shown in connectionlwith the spur line of Fig. 1; Fig. 4 shows an arrangement of networks for terminating a power line; and Fig. 4a shows a terminating network for a three-phase line. In Fig. 1 the line L represents the main transmission line of a power system extendingffrom a generator station A to a station B at which there is a power load. Connected with the main line at s C is a spur line that extends to another power load at station D. I and 2 represent carrier apparatus that may be of any well known type for the transmission of carrier frequency signals over the line. L. 'I'he carrier apparatus may be coupled to the lpower line by means of coupling condensers 3 and 4 and 3 and 4. Since carrier apparatus is gen-j erally designed to match the impedance of the power line, a proper high frequency termination is. obtained wherever carrier apparatus is con nected to the power line. As will later be shown.

30 a point where carrier apparatus is not connected to the power line, other expedients may be employed; Connected in'series with the vline conductors at station A are the networks l0 and il, each of which may be similar tothe network I2 35 which will be described hereinafter. 'I'he purpose of the networks I0 and I I is to eifectively increase the impedance of the power generator at carrier. frequencies-to prevent a dissipation of the carrier 40 I I', similarto I0 and I I, are connectedto the conductors of line l I at station B. By inserting networks, such as I 0 and il, in serieswith the line conductors, the said line, when lookingvin the di. rection of the generator, is causedjtohave a high 4 impedance at the carrier frequenci d the of properly designed carrier ap Y, tus-provides a smooth termination for the carriernequency cur rents employed. Similar networks at station B serve the same purpose as networks III and Il, soV that the transmission of carrier bythe apparatus I and 2 will be free from d iieities' inherentl incarner signaling overl pwer'lines in are not employed/1 yThe eifect upon carrier signaling of the im. pedance represented by the spur line co-nnected with the main transmission line at C is prevented by the insertion of carrier frequency impedance networks in series with the conductors of the spur line. In the arrangement shown, it is assumed that the impedance networks can be placed at the junction of the spur line withv the main line. To obtain a. low impedance for the power frequencies it is necessary touse :a shunt terminated lter whose -shunt member includes an inductance connected directly across the two sis'tance I4 is made at least equal' to the iterative impedance ofthe filter section. A spark gap' I6 serves to protect the entire network. The network I2 uses a high pass lter structure. I t may be designed to present in the power conductor a constant resistance of suitable value over the range of carrier frequencies employed.

Another impedance network of the high pass type is shown in Fig. 2 and a band pass type in Fig. 3;

4either of the latter types may be substituted for Vthe type represented by I2 ofFig. 1, if desired.

" v Fig. 4 shows a mode of treatment of the spur line when it is not "desired to insert i the series high impedance networks in the spur'line at the' junction with the mam une.

In su'ch a case, high impedance networks I 0 and II, which :may be similar to I2 of Fig. 1`, or to Fig. 2 or Fig.- 3, Vare j inserted in series with the spur line conductors nea the point of connection of the power load D', thus Vrendering the power load a high impedunce at carrier. frequencies. In some casesL1 the' networks I0 and-II of Fig. 4 might consist of an inductance shunted by a condenser, o'r if the impedance of the power apparatus at carrier frequencies is high, theymight be omitted entirely.

- To eifect a-smoothotermination of the spur lin'e throughout the range of carrier frequencies employed, 'a network 3 may be bridged across'the spur line conductors. A'I'hat networkcomprises condensers 4. 5, 6 and 1,' an inductance` 8, and a resistance 9, which will be recognized as constituting a filter structure with terminatingresistance.' -Preferably the resistance v9 is made substantially equal to the iterative impedance of the filter. Thus network 3 terminates the line L in an impedance that is equal to the characteristic impedance of the line throughout the range. of carrier frequencies employed. Under 'the arrangement of'Fig.l4 carrier currents now in the spur line. /makes it possible to connect one or more sets o carrierlapparatus preferably vof high impedance, to the spur circuit.

mythe sake of simpneity the terminating net-l work in Fig. 4 has been disclosed as applied to two wires of apower circuit. These wires may be parl: of ;a multi-phase line. Fig. 4a shows a network forterminatinga l three-phase line at highfrequencies. In Fig.l 4a the condensers 20, 2|, za, u, the mancante ze, and resistance 2s are connected across the phase ab; condensers 5 I8, 20, 22 and 23, the inductancel, and resistance 28 are connected across the phase bc: and

4the condensers I9, 2|', 22 and`24, inductance 21,

and resistance 30 are connected across the phase ac. Other well known types of high pass or band pass lter structures may be used in Fig. 4 and Fig. 4a if desired.

It is desirable to point out that the terminating networks shown in Figs. 4 and 4a may be advantageously employed in reducing the effect upon a; powersystem of high frequency transient currents that result from short circuits, light- Y ning, or other causes in or adjacent to.such sys- 10 tem. Such networks may be inserted in a power line at the terminals or other points where impedance are present. Since those networks effectively terminate the`line in an impedance simulatingthe characteristic impedance of the line throughout the higher frequency range, they prevent the building up of high potentials by-resonance action when the line is shocked by transients, lightning, etc. No loss is introduced by the networks to the power currents. While the invention has been disclosed as embodied in certain forms, it is tov be understood that such showing is purely schematic an is not intended to limit theinvention, as dene in the following claims.

What is claimed is:

1..In a'system for the simultaneous transmis` sion of low frequency currents and carrier frequency signaling currents, the combination with a main transmission line, of power apparatus 'connected with the ends of that line. carrier frequency signaling apparatus also connected with the said line at or near the ends thereof, an impedance network connected in series with each ..5 conductor of said main line between each carrier signaling apparatus andthe adjacent power apvparatus to adjust the impedance of the line looking toward the said power apparatus so that the said impedance will be high for carrier frequencies, a spur line connected'with said main line 40 between the points of connection of the carrier apparatus therewith, and a network connectedl with eachof the conductors of the spur line, at

or near the junction with the main line, the net Y work being a high pass mier section terminated 4" in'. a resistance equal to the iterative impedance of the iilter section, the said network presenting a constant resistance over the band of carrier `frequencies. 5o 2. In a system for the transmission of carrier frequency signaling ciments over a power line,

the combination with a power line ofan Aimpedance network connected in series with a conduc.

tor thereof and comprising a wave lter section of the f type, one pillar of the.' being connected in series with the said conductor, and the other pillar being shunted by a resistance atleast equal to the iterative impedance of filter section. f*

-- 3. Inasystem for the on of carriere frequency signaling currents over the conductors of a power line, thecombination with a-carrier circuit derived from the power line conductors; of networks connected in series with at least seme of the power conductorswhich branch awayrom g5 said carrier-circuit, each of said networks includ-' ing a'wave filter section which is terminated-in a 'resistance substantially equal 'to 'the iteativen impedance of the`lter section, and which has a shunt element in 'series with'th'e power conducto tor, each network being designed to insert in series with the power conductor a uniformlyhigh impedance throughout a predetermined-ranged carrier frequenciesv and a low, impedance' for powerfrequencies. l .Y v 7c -mamune, impedance networks connected in the cutoff of said lter section lying below the lowest carrier frequency transmitted over thesystem.

5. In combination, a circuit for the transmission of carrier frequency signalling currents and an impedance network connected in series with each conductor of said circuit, each of saidnetworks comprising a wave vrilter section consisting of at least three impedance elements arranged in v1| formation, one pillar of the 1r being connected in series with the main circuit, and the other pillar being shunted by a resista-nce at least equal to the iterative impedance of the section.

6. The combination with a main transmission line for the simultaneous transmission of lowfrequency currents and carrier-frequency signaling currents, of a spur line bridged across said quency channels.

series with the conductors o! said bridged line,

each of said networks comprising an inductance l, in-series with a conductor of said line shunted by a condenser in series with another inductance and a resistance, substantially equal to the iterative impedance of the said network, connected in shunt with said other inductance, the impedance introduced in said conductors by said networks being uniformly high over a predetermined frequency range.

7.- In combination, a circuit for the transmission of carrier-frequency currents, and impedance networks, one of which is connected in series with each conductor of said circuit, each of said 15 networks comprising a wave lter section which is terminated in a resistance approximately equal to its iterative impedance and which has a shunt element in series with'a conductor of said circuit,

each of said networks having a uniform high 20 impedance over a range oi' frequencies sumoiently wide to accommodatea plurality of carrier-fre- HERMAN A. AFF'EL. ESTIIL I. GREEN. 

